1. Field of the Invention
In regenerative heat exchange apparatus a mass of heat exchange material commonly comprised of packed element plates that form a heat absorbent matrix are positioned in a hot gas passageway to absorb heat from hot gases passing therethrough. After the plates become heated by the hot gas they are suspended in a passageway for cool air where the heated plates transfer their absorbed heat to the cool air flowing therethrough.
As the hot exhaust gases are directed through the heat exchange apparatus, fly ash and unburned products of combustion carried by the exhaust gas are deposited on the surface of the packed element plates, and these deposits continue to be deposited and to build up until air and gas flow through the heat exchanger is substantially stopped. Heat is then generated in the element itself until the deposits begin to glow and cause a "hot-spot," that if not detected will rapidly increase even more until the metal of the heat exchanger will itself ignite and cause a catastrophic fire.
2. Description of Prior Art
Recent developments in the use of infra-red ray detection apparatus to detect "hot-spots" in a heat absorbent matrix of an air preheater in the manner disclosed by the U.S. Pat. No. 3,861,458 of 1975 and No. 3,730,259 of 1973 have been successful in fulfilling their stated objective of signalling a potential fire or "hot-spot" well in advance of the occurrence of a damaging fire.
In actual use, however, it has been found that placing an infra-red ray detector in an air preheater also subjects the detector to a constant flow of corrosive gases and particulate matter. A viewing means including a lens therefor exposed to such an atmosphere quickly becomes clouded with a resulting loss of viewing efficiency. Therefore, it has been determined that any response of such apparatus to a variation in infra-red rays being emitted by a "hot-spot" is also dependent upon the cleanliness of the viewing device.